Radiation therapy, or radiotherapy, is the medical use of ionizing radiation to control malignant cells. In intensity-modulated radiation therapy (IMRT), the intensity or segment of the radiation is modified in accordance with a treatment plan to deliver highly conformal radiation doses to the patient target volume (PTV) of malignant cells, while sparing the surrounding organs at risk (OARs) and other healthy tissues from radiation damage. By dividing the PTV and OAR volumes into individual volume elements (or “voxels”), the IMRT treatment plan can be characterized by a three dimensional dose distribution that characterizes the magnitude of radiation at each of the voxels. An effective two dimensional representation of the dose distribution is the dose volume histogram (DVH).
The development of an intensity-modulated radiation therapy (IMRT) treatment plan (or simply “IMRT planning”) typically involves a complex optimization procedure by which the radiation beam angles and strengths are designed to achieve required dose of radiation for the patient target volume, as well as limit the radiation delivered to neighboring normal tissues as prescribed. While a portion of the IMRT planning process may be performed via computerized optimization algorithms, typically much of the process requires the input and expertise of a human planner.
In particular, the human planner is typically responsible for manually adjusting planning dose objectives (e.g., dose limits, dose volume histogram [DVH] limits, etc.) via a time-consuming, iterative trial-and-error process. The trial-and-error nature of the process is due to the fact that the planner does not know whether or not a set of given dose objectives will result in a plan that meets all physician-prescribed goals for sparing organs at risk (known as “sparing goals”), or when it does, whether tradeoffs between patient target volume (PTV) coverage and sparing of organs at risk (OARs) can be further improved.
Further compounding the process is the fact that physician-prescribed sparing goals are often adapted from clinical trial studies for general populations (e.g., the Radiation Therapy Oncology Group's (RTOG) sparing goals, the QUANTEC (Quantitative Analysis of Normal Tissue Effects in the Clinic) toxicity data, etc.) that ignore specific anatomical, geometric, and demographic information for individual patients, and often represent the upper limit of an organ's dose tolerance rather than an individual patient's lowest achievable dose in that organ. Moreover, because of the lack of quantitative tools for linking variations in anatomy to variations in OAR sparing doses, planners must rely on personal experience and expertise when making adjustments for individual patients.
What is needed, therefore, is a method of predicting intensity-modulated radiation therapy (IMRT) treatment planning parameters that account for anatomical and other variations between patients, without relying entirely on human planner judgment.